Hydrometallurgy is the art of recovering metals from ores by first effecting solution of the metals in the form of a salt, separating the solution from the impoverished solid, then decomposing the metallic salt in such a way as to cause precipitation of the metal in a state of comparative purity. The leaching solution or lixiviant for reclaiming gold and silver from a bed of low-grade ore generally constitutes aqueous solutions of sodium cyanide mixed with oxygen (air) to convert the noble metal (M) to soluble NaM(CN).sub.2, from which M can be recovered either by precipitation with zinc dust or aluminum powder, carbon absorption, or by electrowinning. Sulfuric acid or sulfuric acid-ferric sulfate is the principle practical copper mineral lixiviant.
U.S. Patent Application Ser. No. 116,465, filed on Nov. 3, 1987 by Richard G. Krauth for "CONTROLLED PERCOLATION SYSTEM AND METHOD FOR HEAP LEACH MINING," discloses a highly efficient system and method for heap leach mining. The system includes a plurality of in-line emitters for distributing the leaching solution over a bed of ore in a closely controlled and uniform manner. When one or more of these emitters becomes clogged, it is necessary to remove and clean each clogged emitter or replace it with the new one. Failure to do so can result in a lowered efficiency in the mining operation.
Further, emitters of this type are each designed for one specific flow rate. Thus, when it is desired to change such flow rate due to a change in environmental conditions, for example, the emitter must be replaced for this purpose. Further, it may be prove desirable to vary the flow rates of the emitters positioned at different locations on a pad due to varying depths of the pad, for example.